Completed Rank Scores

README.md

@@ -1,9 +1,47 @@
 # Sql2
 
 Problem 1 : Rank Scores		(https://leetcode.com/problems/rank-scores/ )
+Solution:
+
+Select score, DENSE_RANK()
+OVER (ORDER BY score DESC) AS 'rank'
+from Scores
 
 Problem 2 : Exchange Seats	(https://leetcode.com/problems/exchange-seats/ )
+Solution:
+
+SELECT (
+    CASE 
+       WHEN MOD(id,2) != 0 AND id = cnts THEN id
+       WHEN MOD(id,2) != 0 AND id != cnts THEN id+1
+       ELSE id-1
+    END
+)AS 'id', student FROM seat, (SELECT COUNT(*) AS 'cnts' FROM Seat) AS seat_counts
+ORDER BY id
 
 Problem 3 : Tree Node		(https://leetcode.com/problems/tree-node/ )
+Solution:
+
+Select id, (
+    CASE
+        when p_id IS Null 
+        then "Root"
+        when id In (Select Distinct p_id from tree ) then "Inner"
+        else "Leaf"
+    end) AS type
+from Tree
+order by id ASC
 
 Problem 4 : Deparment Top 3 Salaries		(https://leetcode.com/problems/department-top-three-salaries/ )
+Solution:
+
+SELECT d.name AS Department, e.name AS Employee, e.salary AS Salary
+FROM Employee e
+JOIN Department d ON e.departmentId = d.id
+WHERE 3 > (
+    SELECT COUNT(DISTINCT e2.salary)
+    FROM Employee e2
+    WHERE e2.departmentId = e.departmentId
+      AND e2.salary > e.salary
+)
+ORDER BY d.name, e.salary DESC;